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Wild About Illinois Spiders!

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Spiders belong to a large animal group, the arthropods, all of which have jointed legs and an exoskeleton. Other arthropods include insects, millipedes, centipedes, ticks, harvestmen, scorpions and crustaceans. The arachnid group of arthropods, composed of the spiders, scorpions, harvestmen and ticks, all have eight legs and some of them have book lungs. Spiders are unique, though, in having spinnerets at the end of their abdomen. Spiders also have complex reproductive structures. More than 630 species of spiders have been identified in Illinois so far. Spiders are found in nearly all Illinois habitats, even on and sometimes in water, and are important predators of insects.

Text words in bold are defined in the glossary.

Use the links in the "Gallery" section to see some of the spiders found in Illinois.

Gallery by Family and Species

​Family Agelenidae - These spiders sit at the end of their funnel-shaped web as they wait for insects. Webs are often seen in late summer and early fall close to the ground and covered with dew. The female dies in fall after depositing her eggs in an egg sac. grass spider Agelenopsis naevia

Family Amaurobiidae - The night spiders live in holes in trees, houses or other man-made objects and are active at night. Their web usually is built to open into the hole. The female spins a closed chamber for her eggs and encloses herself in it. After the spiderlings have hatched, they eat her! black lace-weaver spider Amaurobius ferox

Family Corinnidae - Known as sac or swift spiders, these roving predators often build their sac web on trees, other plants or in leaf litter. Their body is about three times as long as it is wide. Some of these spiders are mimics of ants and velvet ants. ant-mimic spider Castianeira amoena

Family Gnaphosidae - The ground spiders are small, usually less than one-half inch in length. They are active at night and hide during the day in such places as under rocks, under logs and in leaf litter. There are more than 2,000 species recognized in this family. These predators run down their prey instead of catching it in a web. ground spider Drassyllus lepidus

Family Linyphiidae - Sheet weavers are very small spiders that build a flat or dome-shaped web. They hang under the web waiting for prey to walk across it, then bite through the web to catch the prey. Most of these species are active at night. There are more than 4,000 types of sheet weaver spiders in the world. black-tailed red sheetweaver Florinda coccinea filmy dome spider Neriene raidiata

Family Lycosidae - Wolf spiders are very common and have four small eyes below four large eyes. They hunt on the ground, in leaf litter, in trees and on the water. Some dig tunnels or burrows. boulder spider Pardosa saxatilis

Family Mimetidae - Pirate spiders feed mainly on other spiders. These small animals visit the web of other spiders and pluck the strands to imitate a trapped insect or a spider ready to mate. When the owner of the web comes to investigate, it is caught and eaten instead! pirate spider Mimetus notius

Family Oxyopidae- Lynx spiders are hunters instead of web-builders. They often hide in flowers to catch pollinating insects. They have large, spiny bristles on their legs. striped lynx spider Oxyopes salticus

Family Pisauridae - Waiting patiently or actively hunting are both methods used by nuseryweb spiders to capture prey. They are large arachnids, and some hunt on water. They may eat tadpoles and small fishes as well as insects. The female carries the egg sac with her and constructs a nurseryweb when the spiderlings are due to hatch. The spiderlings stay in the nuseryweb, guarded by their mother, for about one week and then disperse. sixspotted fishing spider Dolomedes triton

Family Sicariidae - These six-eyed spiders use a sheet web to capture insects. Often living in houses, the brown recluse has a venomous bite. Bites generally occur when people put on clothing or use a towel in which a recluse is resting. brown recluse Loxosceles reclusa

Family Tetragnathidae - These spiders have large fangs that are used in mating. They build orb webs over water. Some are commonly found along creeks and ponds, where they eat many mosquitoes and midges. longjawed orbweaver Tetragnatha guatemalensis

Family Thomisidae - These spiders resemble crabs in the way their legs are positioned. Instead of using a web, they wait in flowers then capture prey directly. whitebanded crab spider Misumenoides formosipes crab spider Misumessus oblongus

Anatomy

​A spider’s body is divided into two main sections: the prosoma (or cephalothorax) and the abdomen. The prosoma is the front part of the body and is composed of the fused head and thorax covered by the hard carapace. The bottom covering of the prosoma is the sternum. Eyes, legs, pedipalps, mouthparts, brain and stomach are all attached to or in the prosoma. The abdomen contains the heart, most of the digestive tract, the reproductive organs, book lungs and the silk glands that open on the spinnerets at the end of the abdomen. The prosoma and abdomen are joined by a narrow stalk, the pedicel.

Eight walking legs are present in spiders. Each leg has seven segments. The segment most distant from the body has two or three claws. Hunting spiders often have thick brushes of specialized hairs at the end of the legs that allow them to cling to smooth surfaces.

Pedipalps look like short legs and are used to clean and handle prey, assist in web building, hold the egg sac, communicate, and store and transfer sperm (males). The two chelicerae are positioned in front of the mouth. Each has a fang and opening of the poison duct. The fang pierces prey and poison is injected. Almost all spiders have poison glands.

Most spiders have eight eyes in characteristic patterns. The eyes of most species only detect movement but may be arranged to detect movement in all directions.

Spiders have two types of respiratory organs, the book lungs and the tracheae. The book lungs consist of thin lamellae for gas exchange and look like the pages of a book. Many spiders have one pair of book lungs while others have two pairs. The slit-shaped openings to the book lungs are on the ventral side of the abdomen near the pedicel. Tracheae are hollow tubes with many branches for moving oxygen to the organs and carrying carbon dioxide away. The tracheae open in a spiracle, located close to the spinnerets in most spiders.

Each spinneret has several or numerous spigots, which are openings for the silk glands. Different types of silk are made in different types of silk glands and for different reasons: webs; snare; retreat; egg sac; dragline. Most spiders have six spinnerets.

Spiders use complex organs to transfer the sperm from the male to the female. The male sperm-transfer organ is located at the end of the pedipalp. The female has a set of ducts and sperm-storage containers between the book lungs on the ventral side of the abdomen. The female reproductive organ, the epigynum, can be seen as a darkened spot on the abdomen.

Since the exoskelton is hard, it does not grow as the spider grows and must be shed. The molting process occurs periodically, usually eight to 12 times before reaching adulthood. If the spider feeds a lot and grows rapidly, molting occurs fairly often, as much as every few weeks. Before molting, the spider stops feeding. It molts in a retreat or suspended by a silk thread. Spiders are very vulnerable to predators when molting.

Life History

​Spiderlings exiting the egg sac look like adults, only smaller, and can build webs and hunt immediately. They feed, grow and molt until reaching adulthood, when the reproductive organs are mature. At this point, most males stop hunting and feeding, although females continue to eat.

Adult males spin a small, triangular web on which they release a drop of semen (containing sperm). The semen is placed in the male reproductive organ in the pedipalp. Males search for females who are ready to mate, guided by chemicals released by the female. When a receptive female is found, the male must communicate to her through courtship that he wants to reproduce, or he takes a chance on being her next prey item. Depending on the species, he may send vibrations as signals (pull on threads of the web, drum his legs on the substrate) or wave his legs and pedipalps. Once he receives the proper reply, he proceeds to transfer the sperm from the pedipalp into the openings of the epigynum. The female makes a silken egg sac and deposits hundreds of eggs in it. The egg sac may be carried with her, deposited in a safe place, or in some species, guarded. If insects are abundant and weather conditions are favorable, females may make several egg sacs in one season.

Sometimes the female eats the male after he finishes transferring the sperm. Most adult spiders die soon after reproduction. In cool climates, spiders may overwinter in the egg stage. Some hibernate as immatures. The natural life span is one or two years.

Webs

​All spiders are predators, but not all of them build webs to catch prey. Those that do build webs have three claws at the tip of each of the eight legs. Most have four to six different types of silk glands in the abdomen. Silk is liquid protein that becomes solid when it is drawn out of the spigots on the spinnerets.

There are many different types of webs. Orb webs are those most often thought of as typical spider webs. The orb web is anchored to plants by frame threads. Radii are placed from the center to the edge, like spokes on a wheel. Then a temporary spiral is added, soon to be replaced by a sticky spiral. Insects fly into the sticky web, are trapped and then captured by the spider. The prey may be wrapped in silk and eaten later. Orb-weaving spiders replace their web once every 24 hours. Some orbweavers may build only half of a web. The bola spiders use a single thread of silk with a drop of sticky glue at the end to swing against flying insects.

Cob web spiders build irregularly shaped webs that may be placed in plants or even in houses. Insects get caught in the threads, and the spider runs out to throw sticky silk on the prey.

Funnel webs are built as a horizontal triangle that ends in a funnel where the spider hides. Sheet web spiders build a flat sheet web with other web threads above and below it.

Spiders and Humans

Spiders are very beneficial to humans, particularly through insect control. Silk threads of cob web spiders have been used in optical instruments. Spider venom is used in research for drug development. Spiders have also been used to study the effects of weightlessness in space and the hazards of drug use.

Most spiders do not bite humans. Although some spiders are large enough to puncture human skin, the bite in most cases causes no problems at all. There are only two spiders in Illinois that are considered to have a dangerous bite: the brown recluse (Loxosceles reclusa) and the black widow (Latrodectus mactans). No bites have been attributed to the northern black widow (Latrodectus variolus), a species that lives in forests.

The brown recluse may live in houses. Bites generally occur when clothing, bedding or towels containing the spider come into contact with human skin. Some bites show no severe effects. Others may cause a red welt to rise, followed by a crust that falls off. It may take several months for the wound to heal. This long-legged species has a dark brown marking in the shape of a violin on the cephalothorax.

The black widow builds a web under objects in outbuildings, trash piles and other similar locations. Male black widow spiders roam about and do not bite, but the female generally stays at the web and will bite if provoked. The bite may not be noticed, but severe abdominal pain, sweating, swollen eyelids, muscle pain and other symptoms will arise. The person usually recovers within a few days. Antivenin is available. The female of this species is about a half-inch long with black coloration and a red hourglass shape on the abdomen.

If bitten by any spider, try to catch the spider and preserve it. Do not pick up the spider. Put a container over it to entrap it. Once it is settled inside the container, turn the container over and add rubbing alcohol to kill and preserve the spider for later identification and cover the container with a lid. Call your local poison control center or physician should you have any reaction to the bite.

• Some spiderlings travel by ballooning. They climb to the top of shrubs or tall grasses and release silk from the spinnerets. Wind currents pick them up and disperse them. In the fall of the year on sunny, windy days, masses of ballooning spiders are often seen.

• Spiders are prey for many other species. To reduce their risk of being eaten, spiders are often camouflaged to match their surroundings. They may also drop out of the web and play dead. Warning coloration is used by other spiders, such as the brightly contrasting black and red coloration of the black widow.

• The mud dauber wasp catches spiders, stings and paralyzes them, then takes them into the mud chambers of her nest. This wasp will place a single egg on each living spider. When the eggs hatch, the larvae feed on the spider, eventually killing it. Other fly and wasp species attack spider egg sacs.

• Fishing spiders can stay under water for up to 40 minutes.

• A jumping spider can jump 20 times its own body length.

• When a web is taken down by a spider, the old web material is eaten. Studies have shown that the protein from the old, eaten web can reappear in newly produced silk in about 30 minutes.

• Spiders spit digestive enzymes on or in prey to digest tissues. They suck in the resulting liquid and the prey’s body fluids.